diff --git a/utils/TableGen/ClangDiagnosticsEmitter.cpp b/utils/TableGen/ClangDiagnosticsEmitter.cpp
index 9f076073eda..60e67c46746 100644
--- a/utils/TableGen/ClangDiagnosticsEmitter.cpp
+++ b/utils/TableGen/ClangDiagnosticsEmitter.cpp
@@ -187,11 +187,13 @@ void ClangDiagsDefsEmitter::run(raw_ostream &OS) {
 // Warning Group Tables generation
 //===----------------------------------------------------------------------===//
 
+namespace {
 struct GroupInfo {
   std::vector<const Record*> DiagsInGroup;
   std::vector<std::string> SubGroups;
   unsigned IDNo;
 };
+} // end anonymous namespace.
 
 void ClangDiagGroupsEmitter::run(raw_ostream &OS) {
   // Compute a mapping from a DiagGroup to all of its parents.